The present disclosure relates to heat exchangers, systems, methods, and devices for performing an energy intensive reaction, either exothermic or endothermic. The devices disclosed herein are particularly applicable to steam/hydrocarbon reforming, and can also be used in other applications. Generally, the system may be used to generate electricity by reforming a mixture of steam and hydrocarbon fuel in a fuel processor that outputs hydrogen gas to a fuel cell. The method for forming the heat exchanger may include diffusion bonding of a stack of alternating shims of appropriate design. The heat exchanger can be used in a reactor usable in connection with different types of fuel cells, e.g., proton-exchange membrane fuel cell (PEMFC) and solid oxide fuel cell (SOFC), to generate electricity in an effective and low cost manner. The device may also include a counter-flow configuration and/or lateral heat transfer between reactant gases and combustion gases to enhance thermal flow and overall efficiency.
Fuel cells serve as a popular alternative to other energy sources due to their high efficiency and relatively benign reaction byproducts. Fuel cells produce electricity through an electrochemical reaction between a fuel input and an oxidant. Many fuel cells to date have been designed to use hydrogen as the fuel input. However, storing large quantities of needed hydrogen gas for the fuel cell has often proved to be impracticable. To address the known disadvantages of hydrogen gas storage, systems to produce hydrogen gas on-demand have been developed.
One type of fuel processor system generates hydrogen on-demand by reforming a hydrocarbon fuel into usable hydrogen. The hydrocarbon fuels used by this fuel processor system are easier to store using existing storage infrastructure relative to hydrogen gas. Reforming hydrocarbon fuel into hydrogen gas requires steam to oxidize the hydrocarbon fuel into carbon monoxide (CO) and hydrogen (H2), typically in the presence of a catalyst. Steam reforming is also a strongly endothermic reaction that must be performed at high temperature to improve the yield of hydrogen gas produced. Therefore, effective thermal management between reactant gas and combustion gas flowing within a fuel processor system is crucial to maintain reaction temperatures.
Current fuel processor systems include a fuel processor which receives a reformate input (steam and hydrocarbon fuel reactant mixture) and produces a syngas output (hydrogen and carbon monoxide). In some known systems, the hot combustion gas flows in channels that are perpendicular (i.e. at a 90° angle) to the channels through which the reformate input flows, a configuration referred to as a cross-flow panel configuration. In other known systems, the hot combustion gas flows in the same direction as reformate input along parallel channels, also known as co-flow. In yet other known systems, the hot combustion gas flows in an opposite direction to reformate input along parallel channels, a configuration referred to as counter-flow. Counter-flow may be a preferred method for reactions having a large temperature differential between hot combustion gas and reactant gas. Counter-flow is believed to be more advantageous than a cross-flow or co-flow configuration because it enables more efficient lateral heat transfer between reactant gases flowing within reaction channels and combustion gases flowing within combustion channels.
Current heat exchangers present many limitations, including high fabrication costs, large size, and sensitivity to carbon formation. These heat exchangers are also expensive to make. One reason for the high fabrication expense is the number of high-skilled welds, both internal and external, that are required. For example, pressure welds are currently used to fabricate fuel processors. A large number of high-skilled pressure welds are required to assemble reactor panels into panel sets and then panel assemblies.
It would be desirable to provide heat exchangers that are easier to make, less costly, and less sensitive to carbon formation. These heat exchangers may provide lateral heat transfer between reactant gases and combustion gases to enhance thermal flow and overall efficiency. The heat exchangers may be used as fuel processors for steam reforming or similar reactions.